Miniaturized unit fuel injector

Abstract

A unit injector (2) of the cam actuated, open nozzle type is disclosed in which an extremely compact injector body (4) has a minimum number of internal flow passages (66, 72) designed to reduce the complexity and cost of manufacture of the injector. The invention is characterized by an injector body (4) having an exterior shape designed to form a fuel supply flow path (22) and an isolated fuel drain flow path (24) between the exterior surface of the injector body (4) and the interior surface of the recess (6) in which the injector (2) is designed to be received. This arrangement allows a very simple pattern of radial passages (66, 72) to be formed in the injector body (4) even through the injector (2) is designed to provide scavenging fuel flow previously requiring a much more complex injector design.

I claim: 
     
       1. A fuel injector for use in an injector receiving recess of an internal combustion engine for injecting periodically into a combustion chamber of the engine a portion of the fuel received from a supply port opening into the recess and for returning the remaining portion of the fuel received from the supply port to an axially spaced drain port which also opens into the recess, said fuel injector comprising: (a) an injector body shaped to be inserted into the recess to form a supply flow path extending between the supply port and the exterior surface of said injector body and to form a drain flow path, isolated from the supply flow path, extending between the drain port and the exterior surface of said injector body, said injector body containing (1) a central bore, and   (2) an open injection orifice located adjacent the inner end of said central bore;     (b) supply connecting means providing a pathway for fuel under pressure to flow from the supply flow path into the central bore, said supply connecting means containing a supply passage extending from the exterior surface of said injector body to the interior surface of the central bore along a straight radial path perpendicular to the longitudinal axis of said injector body;   (c) drain connecting means for providing a pathway for fuel to flow from the central bore into the drain flow path; and   (d) an injector plunger mounted for reciprocal movement within the central bore between an innermost position in which the injection orifice is closed by the inner end of said injector plunger and an outermost position in which an injection chamber is formed within the central bore between the inner end of said injector plunger and the open injection orifice, said injector plunger including flow control means for forming a scavenge flow path to cause a scavenging and cooling flow of fuel from said supply passage, through said central bore and out of said injector body whenever said injector plunger is less than a first predetermined axial distance from the innermost position and for allowing fuel to be metered into the injection chamber from the supply passage whenever said injector plunger is moved more than a second predetermined axial distance from the innermost position.   
     
     
       2. A fuel injector as defined in claim 1, in which said flow control means includes an annular groove on the exterior surface of said injector plunger for forming the scavenge flow path extending axially from the supply passage to the drain passage whenever said injector plunger is in the innermost position and a cylindrical land cooperating with the interior surface of the central bore to form a seal between the scavenge flow path and the injection chamber. 
     
     
       3. A fuel injector as defined in claim 1 or 2, in which and drain connecting means includes a drain passage extending from the exterior surface of said injector body to the interior surface of the central bore along a straight radial path perpendicular to the longitudinal axis of said injector body. 
     
     
       4. A fuel injector as defined in claim 2, in which the shape of the supply passage defined by said supply connecting means is chosen to cause the amount of fuel metered into the injection chamber during each injection cycle to be dependent on both the pressure of the fuel supplied through the supply port and the total time during which said injector plunger is more than the first predetermined axial distance from its innermost position. 
     
     
       5. A fuel injector as defined in claim 2, in which the first predetermined distance is less than the second predetermined distance by an amount equal to the axial extent of said cylindrical land plus the axial extent of the opening of the supply passage into the central bore. 
     
     
       6. A fuel injector as defined in claim 1, in which said injector body contains on its exterior surface first and second annular recesses axially spaced along said injector body to communicate with the supply port and the drain port, respectively, when said injector body is operatively positioned within the injector receiving recess. 
     
     
       7. A fuel injector as defined in claim 6, further including seal means for forming circumferential seals between the exterior of said injector body and the interior surface of the injector receiving recess to isolate the supply flow path from the drain flow path. 
     
     
       8. A fuel injector as defined in claim 1, in which said injector body includes exterior screw threads on its outer end for mating with interior screw threads on the interior of the injector receiving recess and wherein said injector body contains a socket at its outer end shaped to receive a torque applying wrench.